One of the differences between unicast and multicast IP addresses, is that unicast IP addresses represent a single network device while multicast IP addresses represent a group of receives. IANA has reserved the class D range to use for multicast. The first 4 bits in the first octet are 1110 in binary which means that we have the 224.0.0.0 through 239.255.255.255 range for IP multicast addresses.
Some of the addresses are reserved however and we can’t use them for our own applications.
The 224.0.0.0 – 224.0.0.255 range has been reserved by IANA to use for network protocols. All multicast IP packets in this range are not forwarded by routers between subnets. Let me give you an overview of reserved link-local multicast addresses, I’m sure you recognize some of the protocols:
| Address | Usage |
| 224.0.0.1 | All Hosts |
| 224.0.0.2 | All Multicast Routers |
| 224.0.0.3 | Unassigned |
| 224.0.0.4 | DVMRP Routers |
| 224.0.0.5 | OSPF Routers |
| 224.0.0.6 | OSPF DR/BDR Router |
| 224.0.0.7 | ST Routers |
| 224.0.0.8 | ST Hosts |
| 224.0.0.9 | RIPv2 Routers |
| 224.0.0.10 | EIGRP Routers |
| 224.0.0.11 | Mobile Agents |
| 224.0.0.12 | DHCP Server / Relay |
| 224.0.0.13 | All PIM Routers |
| 224.0.0.14 | RSVP Encapsulation |
| 224.0.0.15 | All CBT Routers |
| 224.0.0.16 | Designated SBM |
| 224.0.0.17 | All SBMS |
| 224.0.0.18 | VRRP |
| 224.0.0.19 – 255 | Unassigned |
You probably recognized OSPF (224.0.0.5 and 224.0.0.6), RIPv2 (224.0.0.9) and EIGRP (224.0.0.10). Once you dive more into multicast you will also encounter PIM (Protocol Independent Multicast) with 224.0.0.13.
IANA also reserved the 224.0.1.0 /24 range for certain applications. Everything in the 224.0.1.0 /24 range can be routed however, unlike the 224.0.0.0 /24 range. Here’s an overview:
| Address | Usage |
| 224.0.1.0 | VMTP Managers Group |
| 224.0.1.1 | NTP |
| 224.0.1.2 | SGI-Dogfight |
| 224.0.1.3 | Rwhod |
| 224.0.1.6 | NSS |
| 224.0.1.8 | SUN NIS+ |
| 224.0.1.20 | Any Private Experiment |
| 224.0.1.21 | DVMRP on MOSPF |
| 224.0.1.32 | Mtrace |
| 224.0.1.33 | RSVP-encap-1 |
| 224.0.1.34 | RSVP-encap-2 |
| 224.0.1.39 | Cisco-RP-Announce |
| 224.0.1.40 | Cisco-RP-Discovery |
| 224.0.1.52 | Mbone-VCR-Directory |
| 224.0.1.78 | Tibco Multicast 1 |
| 224.0.1.79 | Tibco Multicast 2 |
| 224.0.1.80 – 224.0.1.255 | Unassigned |
Many of these applications are never used, if you work with Cisco multicast you will see 224.0.1.39 and 224.0.1.40 when you configure a RP (Rendezvous Point).
Just make sure you don’t use the 224.0.0.0 /24 and 224.0.1.0 /24 range and you will be safe. Just like private and public IP addresses for unicast, IANA has reserved a range of IP addresses that we can use for multicast on our local networks. This is the 239.0.0.0 /8 range. Everything between 239.0.0.0 – 239.255.255.255 is safe to use on your own networks.
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